Primary immune deficiencies (PIDs) are a group of rare disorders of the immune system, resulting in increased susceptibility to infections, autoimmunity and malignancies. The most severe forms of PIDs are fatal, unless immune reconstitution is achieved by hematopoietic cell transplantation (HCT), enzyme replacement or gene therapy. Because of the many disease- and treatment-related variables that may affect outcome after HCT, both careful collection of data in Registries and multicenter collaboration are needed to facilitate analysis of outcome and development of prospective clinical trials. In 2009, the Primary Immune Deficiency Treatment Consortium (PIDTC) was established in North America with the goal of building a nation-wide collaboration to carry-out retrospective, cross-sectional and prospective studies that would define risk factors, long term outcomes and late effects in children with Severe Combined Immunodeficiency (SCID), Wiskott-Aldrich Syndrome (WAS) and Chronic Granulomatous Disease (CGD) who receive HCT or other forms of definitive treatment. In April 2011 the first annual PIDCT Scientific Workshop was held in San Francisco followed by workshops in Boston and Houston in 2012 and 2013, respectively. These workshops have provided a unique and critical forum to assemble experienced and young investigators from all major centers in North America involved in the treatment of these disorders, as well as biostatisticians and Patient Advocacy Groups and has been responsible for initiating the development of national and European collaborations. The proposed 4th annual PIDTC Scientific Workshop in Seattle will focus on new timely topics to further advance the development of clinical trials aimed at improving treatment of PIDs, international collaborations with Asia and South America, and survey studies with Patient Advocacy Groups. The specific objectives of the workshop are: 1) To disseminate information on survival, clinical status, and immune function in patients with severe PIDs who have received HCT or other forms of treatment 2) To initiate data collection and analysis in other forms of severe PIDs that can be treated by HCT 3) To analyze relevance of biological markers that predict successful immune reconstitution following HCT 4) To discuss the results of novel approaches to HCT for PID that may minimize transplant-related toxicity while allowing robust and durable engraftment and immune reconstitution 5) To promote newborn screening and develop optimal treatment protocols for newborns with SCID. 6) To prompt development of clinical trials in the field of HCT for PIDs 7) To promote education of young investigators with a specific interest in treatment of PIDs 8) To increase synergy among Patient Advocacy Groups actively involved in PID awareness campaigns